Course protractor



Jan. 13, 1942. R. s. BLAIR 1 COURSE PROTRACTOR Filed Oct. 29, 1937IIII"IIIIIIIIIIIIIIIIIITII' sunskilled users.

Patented Jan. 13, 1942 UNITED STATES PATENT OFFICE 4 Claims.

This invention relates to course protractors for plotting courses onnavigation charts and the like.

One of the objects of this invention is to provide a simple,inexpensive, and practical course protractor well adapted to meetvarying conditions of use. Another object is to provide a courseprotractor of the above character which will be eflicient and reliablein operation. Another object is to provide a course protractor of theabove character which will be neat and attractive in appearance and yetbe of such sturdy construction as to withstand hard usage. Anotherob-ject is to provide a course protractor of the above character whoseuse will be simple and which may be quickly and easily operated byAnother object is to provide a course protractor of the above characterwhich may be constructed from inexpensive and light materials. Anotherobject is to provide a course protractor of the above character whichwill be inexpensive to manufacture and easily assembled. Another objectis to provide a course protractor of the above character which isaccurate in operation. Another object is to provide a course protractorof the above character which may be operated with a minimum ofadjustments. Other objects will be in part obvious and in part pointedout hereinafter.

The invention accordingly consists in the features of construction,combinations of elements, and arrangements of parts as will beexemplified in the structure to be hereinafter described and the scopeof the application of which will be indicated in the following claims.

In the accompanying drawing in which is shown one of the variouspossible embodiments of my invention:

Figure 1 is a top plan view of the instrument in operating position upona chart;

Figure 2 is a side view of the device shown in Figure 1;

Figure 3 is a vertical sectional view taken along the line 3--3 ofFigure 2;

Figure 4 is an enlarged perspective view of a part of the device shownin Figure 1;

Figure 5 is a detailed assembly view of the part shown in Figure 4; and

Figure 6 is a top plan view of a part of the device shown in Figure 1.

.Similar reference characters refer to similar parts throughout theseveral views of the draw- 111 As conducive to a clearer understandingof certain features of this invention, it might here be pointed out thatprevious devices designed to plot courses on navigation charts have beenaccompanied by excessive cost and inefi'icient operation. Some of thesedevices require numerous manual settings of the instrument before thecourse may be ascertained. This is burdensome to the operator andfurthermore at any time a slight movement of these instruments duringthe various settings will lead to an inaccurate result. Furthermore, theuse of some of these instruments is restricted to the use of a charttable or a flat surface which is not usually available in a small boat.Without such a flat surface these instruments are extremely difiicult tooperate if an accurate course is to be followed. Among the severalobjects of this invention is to provide a device for overcoming theabove-mentioned difficulties as well as many others.

Referring now to the drawing in detail, the instrument generallyindicated at Ill (Figure l) is shown in position upon a section II of anavigation chart. A pivotally mounted arm I2 slides along a body memberI3. Arm I2 is first aligned with a course l4 plotted on the chart and isthen slid along member l3 until its edge crosses the center of compassrose I5. When the instrument is properly aligned, as will be more fullydescribed hereinafter, the user may find the direction of the course I4by noting the direction arm I2 crosses compass rose I5. The arm I2 ispreferably formed of resilient material with a tendency to assume theposition indicated in dotted lines at I2a in Figure 3 of the drawing,or, in other words, to spring upwardly away from the chart or supportingsurface. It can, of course, be readily flattened into the position shownin full lines so as to register with the course or with compass points.

Member I3 is preferably flexible and resilient and both it and itsenlarged end portion I6 are made of metal or from some other lightflexible material such as transparent Celluloid. Secured to the undersurface of end portion I6 and extending up the center of the undersurface of member I3 is a pad I'I (Figures 1, 2, and 3) made of rubberor similar material. The exposed surface of the pad I1 is preferablyroughened (Figure 3) so that when the instrument is placed upon a chartit secures a firm grip thereon and resists lateral movement.

Mounted upon member I3 is a sliding member generally indicated at I8.This sliding member (Figure 4) has two channels I9 and 20 formed uponits outer edges. On one side of member I8 a tongue 2| is cut out ofchannel I9 (Figure 4). This tongue preferably extends out from member I8in the same plane as its top surface 22 and has a portion drawn upwardlyto form tube 23 (Figure 3). Tube 23 is so positioned on tongue 2I thatwhen sliding member 26 is mounted on member I3 the center point of thetube lies directly above the edge 24 of member I3 (Figure 1).

The distance between the inner surface of channels I9 and 20 is greaterthan the width of member I3. A spring 25 (Figure 5) is inserted inchannel and preferably has its ends 26 and 2! turned outwardly toprevent longitudinal movement of the spring when it is in position inchannel 20 (Figure 5). When sliding member I8 is in position upon memberI3, spring exerts a pressure against edge 28 of the body member andholds the inner surface of channel I 9 against edge 24 of the bodymember I3 so that member I8 is always held in alignment with body memberI3 as it slides thereon.

Arm I2 (Figure 6) has a tongue 29 formed thereon. Through this tongueand part of the body of arm I2 is a hole 30. Hole 30 is so positionedthat its center point would be bisected by a line drawn through theouter edge 3I of arm I2. Tube 23 (Figure 3) extends through hole 30,permitting arm I2 to pivot with relation to sliding member I3 on tube 23as a pivot point. A spring washer 33 lies between the turned lip 32 oftube 23 and arm I2. This washer presses downwardly upon the arm andholds it by friction in any desired angular relation with respect tomember I8.

Thus arm I2 may be slid along member I3 and the center point of tube 23coincides with the edge 24 of member I3 (Figure 1). The sliding memberI8 is held in alignment with member I3 by spring 25 and arm I2 has beensecured to the sliding member in such manner that it maintains anyposition desired by the user with respect to members I3 and I8.

Referring to Figure 1, in operation, member I3 is so placed that itsedge 24 crosses the course I4 plotted on the chart and is also alignedwith the center 34 of compass rose I5. Then arm I2 is moved along memberI3 and turned until its edge 3I is in alignment with course It. Thenholding the instrument I0 by its enlarged end portion I6, member I8 isslid along member I3 until the user views the center point 34 of compassrose !5 in the center of tube 23. During this movement arm I2 is held ina definite position with respect to member I8 by spring washer 33.Lateral movement of body member I3 is prevented at this time by rubberpad I? (Figure 3) which extends below the lowermost part of member I8and is held in contact with the chart by the downward pressure exertedby the user while moving arm I2 and member I8. During this movement theends of the arm I2 will, if formed of the curved resilient material ashereinbefore noted, spring upwardly from the surface of the chart andhence avoid contact with folds or irregularities in the surface whichmight alter the angle at which it is set. It is to be understood,however, that if preferred the arm may be used in the fiat form shown infull lines in F;gure 3 of the drawing. When the user views the centerpoint of the compass rose through tube 23, edge 3| of the arm I2 crossesthe compass in a line exactly the same as the course plotted upon thechart and the user reads the direction of that course.

It will now become clear that I have provided a thoroughly practical anddurable course protractor which is so designed that the user can findthe direction of any course with a minimum of eiTort. Furthermore, thedevice is accurate and requires a minimum of manual setting. I have alsoprovided a device which may be easily and efficiently operated by anunskilled user in small boats which do not have plane surfaces such aschart tables upon which to plot courses.

It will thus be seen that I have provided a thoroughly practical courseprotractor in which the several objects hereinabove mentioned as well asmany others are accomplished. As many possible embodiments may be madeof the above invention and a many changes might be made in theembobiment above set forth, it is to be understood that all matterhereinabove set forth, or shown in the accompanying drawing, is to beinterpreted as illustrative and not in a limiting sense.

I claim:

1. In a course protractor, in combination, an elongated body member,means slidably connected to said body member, a resilient member havingupwardly curved ends pivotally connected to said first mentioned means,and means formed on said second member adapted to register with astraight line, said last mentioned means being so positioned on saidsecond member that it may be aligned with any line on a chart or acrossa compass rose.

2. In a course protractor, in combination, a body member, means securedto the under surface of said body member to prevent lateral movementthereof when said course protractor is in contact with a surface, amember slidably mounted on said body member, said member having portionsextending around the edges of said body member and abutting against theunder surface thereof, said means spacing said bodw member from saidsurface whereby said member may be slid along said body member withouttouching said surface, a cross member pivotally mounted on said slidingmember, said cross member having a straight edge adapted to be alignedwith a course or across a compass rose on a chart, and means adapted toyieldingly retain said cross member in diiferent positions upon saidsliding member.

3. In a course protractor, in combination, a body member, an enlargedportion formed on one end of said body member, means secured to theunder surface of said enlarged portion and said body member to preventlateral movement thereof when said course protractor is in contact witha surface, said body member being formed of a resilient metal, a memberslidably mounted on said body member, said means spacing said bodymember from a surface and preventing contact between said sliding memberand a surface when said course protractor is placed on a surface, and across member pivotally mounted on said sliding member, said cross memberhaving a straight edge whereby said cross member may be aligned with acourse or across a compass rose.

4. In a course protractor, in combination, a body member, a straightedge formed on said body member, a member adapted to slide along saidbody member, two projections formed on said sliding member abuttingagainst said straight edge, resilient means on said sliding membercontacting the opposite edge of said body member at a single point, saidresilient means holding said projections in contact with said straightedge, whereby said sliding member is held in alignment with saidstraight edge, a cross member pivotally mounted on said slidin memberand resilient means adapted to yieldingly hold said cross member in anydesired position on said sliding member.

ROBERT S. BLAIR.

